mpi_buffer_detach(3openmpi) [osx man page]

MPI_Buffer_detach(3OpenMPI)											       MPI_Buffer_detach(3OpenMPI)

NAME

       MPI_Buffer_detach - Removes an existing buffer (for use in MPI_Bsend, etc.)

SYNTAX

C Syntax
       #include <mpi.h>
       int MPI_Buffer_detach(void *buf, int *size)

Fortran Syntax
       INCLUDE 'mpif.h'
       MPI_BUFFER_DETACH(BUF, SIZE, IERROR)
	    <type>    BUF(*)
	    INTEGER   SIZE, IERROR

C++ Syntax
       #include <mpi.h>
       int Detach_buffer(void*& buffer)

OUTPUT PARAMETERS

       buf	 Initial buffer address (choice).

       size	 Buffer size, in bytes (integer).

       IERROR	 Fortran only: Error status (integer).

DESCRIPTION

       Detach  the  buffer  currently  associated  with MPI. The call returns the address and the size of the detached buffer. This operation will
       block until all messages currently in the buffer have been transmitted. Upon return of this function, the user may reuse or deallocate  the
       space taken by the buffer.

       Example: Calls to attach and detach buffers.

	   #define BUFFSIZE 10000
	   int size
	   char *buff;
	   MPI_Buffer_attach( malloc(BUFFSIZE), BUFFSIZE);
	   /* a buffer of 10000 bytes can now be used by MPI_Bsend */
	   MPI_Buffer_detach( &buff, &size);
	   /* Buffer size reduced to zero */
	   MPI_Buffer_attach( buff, size);
	   /* Buffer of 10000 bytes available again */

NOTES

       The  reason  that  MPI_Buffer_detach  returns the address and size of the buffer being detached is to allow nested libraries to replace and
       restore the buffer. For example, consider

	   int size, mysize, idummy;
	   void *ptr, *myptr, *dummy;
	   MPI_Buffer_detach( &ptr, &size );
	   MPI_Buffer_attach( myptr, mysize );
	   ...
	   ... library code ...
	   ...
	   MPI_Buffer_detach( &dummy, &idummy );
	   MPI_Buffer_attach( ptr, size );

       This is much like the action of the UNIX signal routine and has the same strengths (it's simple) and weaknesses (it only works  for  nested
       usages).

       For  Fortran:  The Fortran binding for this routine is different. Because Fortran does not have pointers, it is impossible to provide a way
       to use the output of this routine to exchange buffers. In this case, only the size field is set.

       For C: Even though the buf argument is declared as void, it is really the address of  a	void  pointer.	See  Rationale,  below,  for  more
       details.

       Even though the C functions MPI_Buffer_attach and MPI_Buffer_detach both have a first argument of type void*, these arguments are used dif-
       ferently: A pointer to the buffer is passed to MPI_Buffer_attach; the address of the pointer is passed to MPI_Buffer_detach, so	that  this
       call can return the pointer value.

ERRORS

       Almost all MPI routines return an error value; C routines as the value of the function and Fortran routines in the last argument. C++ func-
       tions do not return errors. If the default error handler is set to MPI::ERRORS_THROW_EXCEPTIONS, then on error the C++ exception  mechanism
       will be used to throw an MPI:Exception object.

       Before  the error value is returned, the current MPI error handler is called. By default, this error handler aborts the MPI job, except for
       I/O function errors. The error handler may be changed with MPI_Comm_set_errhandler; the predefined error handler MPI_ERRORS_RETURN  may	be
       used to cause error values to be returned. Note that MPI does not guarantee that an MPI program can continue past an error.

SEE ALSO

       MPI_Buffer_attach
       MPI_Bsend

Open MPI 1.2							  September 2006				       MPI_Buffer_detach(3OpenMPI)

MPI_Buffer_attach(3)							MPI						      MPI_Buffer_attach(3)

NAME

       MPI_Buffer_attach -  Attaches a user-provided buffer for sending

SYNOPSIS

       int MPI_Buffer_attach(void *buffer, int size)

INPUT PARAMETERS

       buffer - initial buffer address (choice)
       size   - buffer size, in bytes (integer)

NOTES

       The  size  given  should  be the sum of the sizes of all outstanding Bsends that you intend to have, plus MPI_BSEND_OVERHEAD for each Bsend
       that you do.  For the purposes of calculating size, you should use MPI_Pack_size .

       In other words, in the code
       MPI_Buffer_attach( buffer, size );
       MPI_Bsend( ..., count=20, datatype=type1,  ... );
       .
       .
       .
       MPI_Bsend( ..., count=40, datatype=type2, ... );

       the value of size in the MPI_Buffer_attach call should be greater than the value computed by
       MPI_Pack_size( 20, type1, comm, &s1 );
       MPI_Pack_size( 40, type2, comm, &s2 );
       size = s1 + s2 + 2 * MPI_BSEND_OVERHEAD;

       The MPI_BSEND_OVERHEAD gives the maximum amount of space that may be used in the buffer for use by the BSEND routines in using the  buffer.
       This value is in mpi.h (for C) and mpif.h (for Fortran).

THREAD AND INTERRUPT SAFETY

       The  user  is responsible for ensuring that multiple threads do not try to update the same MPI object from different threads.  This routine
       should not be used from within a signal handler.

       The MPI standard defined a thread-safe interface but this does not mean that all routines may be called	without  any  thread  locks.   For
       example,  two  threads  must  not attempt to change the contents of the same MPI_Info object concurrently.  The user is responsible in this
       case for using some mechanism, such as thread locks, to ensure that only one thread at a time makes use of this routine.  Because the  buf-
       fer  for buffered sends (e.g., MPI_Bsend ) is shared by all threads in a process, the user is responsible for ensuring that only one thread
       at a time calls this routine or MPI_Buffer_detach .

NOTES FOR FORTRAN

       All MPI routines in Fortran (except for MPI_WTIME and MPI_WTICK ) have an additional argument ierr at the end of the argument  list.   ierr
       is  an integer and has the same meaning as the return value of the routine in C.  In Fortran, MPI routines are subroutines, and are invoked
       with the call statement.

       All MPI objects (e.g., MPI_Datatype , MPI_Comm ) are of type INTEGER in Fortran.

ERRORS

       All MPI routines (except MPI_Wtime and MPI_Wtick ) return an error value; C routines as the value of the function and Fortran  routines	in
       the  last  argument.  Before the value is returned, the current MPI error handler is called.  By default, this error handler aborts the MPI
       job.  The error handler may  be	changed  with  MPI_Comm_set_errhandler	(for  communicators),  MPI_File_set_errhandler	(for  files),  and
       MPI_Win_set_errhandler  (for  RMA  windows).   The  MPI-1 routine MPI_Errhandler_set may be used but its use is deprecated.  The predefined
       error handler MPI_ERRORS_RETURN may be used to cause error values to be returned.  Note that MPI does not guarentee that an MPI program can
       continue past an error; however, MPI implementations will attempt to continue whenever possible.

       MPI_SUCCESS
	      - No error; MPI routine completed successfully.
       MPI_ERR_BUFFER
	      - Invalid buffer pointer.  Usually a null buffer where one is not valid.
       MPI_ERR_INTERN
	      - An internal error has been detected.  This is fatal.  Please send a bug report to mpi-bugs@mcs.anl.gov .

SEE ALSO

       MPI_Buffer_detach, MPI_Bsend

LOCATION

       bufattach.c

								     5/20/2010						      MPI_Buffer_attach(3)